A/C - high low side pressure
 

I have a 93 400e with a factory R134 A/C system.

AC works ok but not get really cold, I'm getting dash vent temps in the low/mid 50's. Sight glass check show refrigerant levels are OK.

My high side pressures seem to be fine - 190 to 250 PSI depending on ambient temps and airflow thru the condensor but my low side pressure seems to be a bit too high. It reads 41-44 PSI. My other cars with R134 systems have low pressure side readings of 30-34 PSI. The compressor cycles on and off but seems to be running about 95% of the time the A/C is on.

I'm thinking a stuck/faulty expansion valve could be causing the high readings... Any other possible causes? Or opinions?

Tim